1. Field
This application is related to gas tungsten arc welding and more particularly to a flux for substantially increasing weld penetration containing one or more compounds selected from the group of compounds consisting of a) a titanium oxide, b) a nickel oxide, c) a metal silicide, and d) mixtures of these compounds. A flux containing at least two titanium oxides, nickel oxide, and a metal silicide is particularly useful for welding a wide variety of materials including nickel-based alloys and carbon and stainless steels.
2. Background
The gas tungsten arc welding (GTAW) process is an arc welding process that uses an arc between a non-consumable tungsten electrode and the work piece to cause -localized coalescence of the base material. The GTAW process is used to produce high quality welds in a variety of materials. Applications include welding of sheet, plate, tube, and castings for use in aerospace, power generation, shipbuilding, and other industries. GTAW can be used with filler metals or consumable inserts to produce welds in thick sections. Autogenous welds (welds without filler metals) can be made in thin sections or for root passes in thick sections.
The primary limitation of the GTAW process is low productivity due to low deposition rates and shallow penetration. The inability of GTAW to produce welds with deep penetration limits the thickness of material that can be reliably joined to less than approximately 0.10 in (2.5 mm) thick. Materials greater than 0.1 in (2.5 mm) thick typically require weld joint preparation and multiple passes to fill the weld joint. GTAW welds are also affected by heat-to-heat compositional variations in the material being welded. While variable penetration is most often encountered in stainless steel and nickel-based alloys, this phenomenon occurs in other materials as well.
A method of increasing both the amount and consistency of penetration in gas tungsten arc (GTA) weldments is to apply a thin layer of flux to the surface of the part or joint to be welded prior to welding. The use of traditional fluxes for the GTAW process is not required since shielding and arc stabilization are provided by the use of an external shielding gas. Fluxes used for GTAW to improve penetration are inherently different than those used for soldering, brazing, or other arc welding processes since they neither clean the surface of the part nor protect the weld pool from oxidation.
The use of flux for increasing penetration in mild steel materials has been described by several authors in the former Soviet Union. An article by E. D. Raimond et al. titled xe2x80x9cWelding of High Strength Steel Using Activating Fluxes in Powder Formxe2x80x9d Svar. Proiz, No. 6, pp. 18-19, suggests that the use of Soviet Flux FS-71 increased GTAW penetration in steel by 50-100 percent No compositional details were given for the flux. A later article by O. E. Ostroviski entitled xe2x80x9cThe Effect of Activating Fluxes on the Penetration Capability of the Welding Arc and the Energy Concentration in the Anode Spotxe2x80x9d Svar. Proiz, No. 3, pp.3-4, 1977, reveals that the composition of flux FS-71 is 57.3 percent SiO2, 6.4 NaF, 13.6 TiO2, 13.6 Ti, and 9.1 Cr2O3. Another paper by L. E. Eroshenko et al, titled xe2x80x9cAn Examiantion of the Glow of Anode Vapors for the Evaluation of the Technological Characteristics of the Arc Running in Argon, Avt. Svarka, 1979, No. 9, pp. 33-35, evaluated the enhanced penetration caused by fluorides of several alkali and alkaline-earth elements. The effects of individual fluorides were studied and the fluorides evaluated in the study were used as a basis for selecting components for titanium and steel GTAW fluxes. A similar approach to the Soviet flux design is described in U.S. Pat. No. 5,525,163 by H. R. Conaway et. al. They claim that the use of 7 to 59 percent LIF promotes penetration in 321 austenitic stainless steel. They infer that this ingredient will promote enhanced penetration in other materials such as carbon steel as well. Paskell describes a flux composed of TiO or TiO2 (50%), Cr2O3 (40%) and SiO2(10%) in U.S. Pat. No. 5,804,792 that is used to increase the penetration in stainless steel.
The flux reported by Ostrovski (FS-71) and flux no.69 reported by Conaway (23.6 Al2O3, 39.4 LiF, 15.7 MgO, 5 B2O3, and 15.7 Fe2O3) were evaluated in the instant effort on Alloy 600 material. Neither flux spread well or produced consistently improved penetration above what was measured without flux. Additionally, these fluxes both contain fluorides which can increase the risk of corrosion in some environments and which generated a considerable amount of fluoride based fume which is can be hazardous as well. Additional experiments were conducted in the present effort to determine whether the addition of material such as Cr2O3 or SiO2 or both as used by Paskell in U.S. Pat. No. 5,804,792 enhanced the penetration characteristics of the fluxes of the present invention detailed in Table 1 below. When SiO2 (10 wt. %) or Cr2O3 (40 wt. %) or both (10 wt. % SiO2 and 40 wt. % Cr2O3) were added to flux Ni106 of the present invention, weld penetration decreased by a factor of about 2 or more.
In order to overcome the various problems encountered with prior art fluxes and find new fluxes that substantially improve flux penetration, it is an object of the present invention to provide a flux composition for use with the GTA process that improves weld penetration in nickel-based alloys and a variety of steels including carbon and stainless steels.
It is an object of the present invention to reduce the cost of the GTA process by reducing the time and effort in joint preparation.
It is an object of the present invention to reduce the number of passes required in a multi-pass gas tungsten arc weld.
It is an object of the present invention to reduce the distortion of gas tungsten arc welds.
It is an object of the present invention to produce welds with mechanical properties that are not degraded through the use of the flux composition.
It is an object of the present invention to produce welds with a weld quality that is not degraded through the use of the flux composition.
It is an object of the present invention to provide a flux that is provided in a variety of conveniently useable forms such as a paint, adhesive, hot melt, rod, stick, or wire.
The foregoing and other objects, features and advantages of the invention will become apparent from the following disclosure in which one or more preferred embodiments of the invention are described in detail. It is contemplated that variations in procedures may appear to a person skilled in the art without departing from the scope of or sacrificing any of the advantages of the invention.
The above objects are met in the present invention by using at least one compound selected from the group of compounds consisting of a) a titanium oxide, b) a nickel oxide, c) a metal silicide, and d) mixtures thereof. A flux consisting of any one of these compounds alone has been found to increase GTAW weld penetration in a wide variety of nickel-based, carbon and stainless steel materials. The titanium oxide can include any of the oxides of titanium including but not limited to titanium monoxide, titanium dioxide, and dititanium trioxide. Considerable weld penetration is achieved when a mixture of at least two titanium oxides, e.g., titanium monoxide and titanium dioxide, is used. For nickel-based alloys, a combination of titanium oxides and nickel oxide has found be quite effective with the addition of manganese silicide further improving weld quality.
In combination, these material appear to have a synergistic effect when employed in combination and in the following amounts: about 15 to about 50 weight % titanium oxide, about 10 to about 50 weight % titanium dioxide, 3 to about 15 weight % manganese silicide and about 20 to about 40 weight % nickel oxide. Two robust compositions applicable to a wide variety of materials including carbon and stainless steels and especially nickel-based alloys consist essentially of: a) about 23 weight % titanium monoxide, about 23 weight % titanium dioxide, about 23 weight % dititanium trioxide, about 23 weight % nickel oxide, and about 8 weight % manganese silicide and b) about 9 weight % manganese silicide about 30 weight % nickel oxide, about 18 weight % titanium monoxide, about 20 weight % titanium dioxide, and about 23 weight % dititanium trioxide.
Any of the above compositions are used by applying them to the weld zone for GTAW in a variety of ways. The fluxes can be mixed with a liquid carrier such as water, an alcohol, a ketone, or an ester among others to form a paste which is applied to the weld zone. They can be included in a cored wire or rod. Or they can be formed on the external surface of a filler wire or rod. One particularly attractive method of delivery is their combination with a wide variety of polymeric binders, both thermoset and thermoplastic including but not limited to polyolefins, vinyls, styrenics, acrylics, urethanes, epoxies, polyethers, polyamides, polyesters, polyimides, cellulosics, and urea and melamine formaldehydes to form 1) adhesives including hot melts and tapes, 2) water and solvent-based paints, 3) films, and 4) sticks, rods, and wires. When incorporated into adhesives such as hot melts and tapes, they can effectively hold the materials to be joined during the welding process.
The foregoing and other objects, features and advantages of the invention will become apparent from the following disclosure in which one or more preferred embodiments of the invention are described in detail and illustrated in the accompanying examples. It is contemplated that variations in compositions and their use in the welding process may appear to a person skilled in the art without departing from the scope of or sacrificing any of the advantages of the invention.